Non-contact mobile charge measurement with leakage band-bending and dipole correction

Abstract

Corona charges are used to bias a wafer to push down mobile charges and then pull them up during temperature cycles. Mobile charge is measured from the drops in the corona voltage due to the mobile charges. Corrections are made in the measurements for dipole potentials, leakage and silicon band-bending.

1. A method for measuring mobile charge in a dielectric layer on a substrate, said method comprising:
 applying at least one first polarity corona bias temperature stress cycle to said layer; 
 applying successive second polarity corona bias temperature stress cycles to said layer and measuring a corresponding voltage drop; and 
 determining said mobile charge according to said voltage drops. 
 
   
   
     2. A method according to  claim 1 , wherein said successive second polarity corona bias temperature stress cycles are of substantially equal time. 
   
   
     3. A method according to  claim 1 , including applying the successive second polarity corona bias temperature stress cycles to said layer and measuring said corresponding voltage drop until the voltage drops approach a terminal value, ΔV Terminal . 
   
   
     4. A method according to  claim 1 , further comprising:
 measuring an amount of charge necessary to bias a leakage monitoring site on said substrate from a midband condition to a pull-up condition before at least one said successive second polarity corona bias temperature stress cycle; 
 measuring an amount of charge necessary to bias said leakage monitoring site back to said midband condition after said at least one of said successive second polarity corona bias temperature stress cycles; and 
 correcting said mobile charge according to a difference between said charge measurements. 
 
   
   
     5. A method according to  claim 4 , wherein said midband conditions are determined by a surface photovoltage measurement. 
   
   
     6. A method according to  claim 1 , further comprising:
 creating a dipole potential monitoring site on said layer with a second polarity corona prior to at least one first polarity corona bias temperature stress cycle; 
 measuring a dipole site voltage at said site before and after at least one second polarity corona bias temperature stress cycle; 
 measuring an amount of charge necessary to bias a leakage monitoring site on said substrate from a midband condition to a pull-up condition before at least one said successive second polarity corona bias temperature stress cycle; 
 measuring an amount of charge necessary to bias said leakage monitoring site back to said midband condition after said at least one of said successive second polarity corona bias temperature stress cycles; 
 measuring a surface photovoltage before and after at least one of said successive second polarity corona bias temperature stress cycles, wherein said successive cycles are of substantially equal time and continue until the voltage drops approach a terminal value; and 
 correcting said mobile charge according to said dipole site voltages, a difference between said charge measurements and said surface photovoltages. 
 
   
   
     7. A method for measuring mobile charge in a dielectric layer on a substrate, said method comprising:
 applying at least one first polarity corona bias temperature stress cycle to said layer; 
 applying successive second polarity corona bias temperature stress cycles to said layer and measuring a corresponding voltage drop; 
 correcting error in said voltage drop using at least one of: a measured change in dipole potentials, a measured leakage of charge, and measured silicon band-bending; and 
 calculating said mobile charge using the corrected voltage drop. 
 
   
   
     8. A method according to  claim 7 , wherein said successive second polarity corona bias temperature stress cycles are of substantially equal time. 
   
   
     9. A method according to  claim 7 , including applying the successive second polarity corona bias temperature stress cycles to said layer and measuring said corresponding voltage drop until the voltage drops approach a terminal value, ΔV Terminal . 
   
   
     10. A method according to  claim 7 , further comprising:
 creating a dipole potential monitoring site on said layer with a second polarity corona prior to at least one first polarity corona bias temperature stress cycle; 
 measuring a dipole site voltage at said site before and after at least one second polarity corona bias temperature stress cycle; and 
 correcting said mobile charge according to said dipole site voltages. 
 
   
   
     11. A method according to  claim 7 , further comprising:
 measuring an amount of charge necessary to bias a leakage monitoring site on said substrate from a midband condition to a pull-up condition before at least one said successive second polarity corona bias temperature stress cycle; 
 measuring an amount of charge necessary to bias said leakage monitoring site back to said midband condition after said at least one of said successive second polarity corona bias temperature stress cycles; and 
 correcting said mobile charge according to a difference between said charge measurements. 
 
   
   
     12. A method according to  claim 11 , wherein said midband conditions are determined by a surface photovoltage measurement. 
   
   
     13. A method according to  claim 7 , further comprising:
 measuring a surface photovoltage before and after at least one of said successive second polarity corona bias temperature stress cycles; and 
 correcting said mobile charge according to said surface photovoltages. 
 
   
   
     14. A method according to  claim 7 , further comprising:
 creating a dipole potential monitoring site on said layer with a second polarity corona prior to at least one first polarity corona bias temperature stress cycle; 
 measuring a dipole site voltage at said site before and after at least one second polarity corona bias temperature stress cycle; 
 measuring an amount of charge necessary to bias a leakage monitoring site on said substrate from a midband condition to a pull-up condition before at least one said successive second polarity corona bias temperature stress cycle; 
 measuring an amount of charge necessary to bias said leakage monitoring site back to said midband condition after said at least one of said successive second polarity corona bias temperature stress cycles; 
 measuring a surface photovoltage before and after at least one of said successive second polarity corona bias temperature stress cycles, wherein said successive cycles are of substantially equal time and continue until the voltage drops approach a terminal value; and 
 correcting said mobile charge according to said dipole site voltages, a difference between said charge measurements and said surface photovoltages. 
 
   
   
     15. A method for measuring mobile charge in a dielectric layer on a substrate, comprising:
 applying a first polarity corona charge over at least one corona bias temperature stress cycle, said first polarity charge being sufficient to move mobile charge to a first boundary surface of said dielectric layer; 
 applying a second polarity corona charge over at least one corona bias temperature stress cycle, said second polarity charge being sufficient to move mobile charge to a second boundary surface of said dielectric layer; 
 measuring a first voltage between the first boundary surface and the substrate substantially contemporaneously with said applying a second polarity corona charge; 
 performing at least one additional corona bias temperature cycle; 
 measuring a second voltage between the first boundary surface and the substrate; 
 calculating a voltage difference between the first voltage and the second voltage; and 
 calculating said mobile charge by summing said voltage difference with at least one of a change in dipole potentials, a change in potential due to charge leakage, and a change in potential due to silicon band-bending. 
 
   
   
     16. A method according to  claim 15 , further comprising:
 performing successive second polarity stress cycles of substantially equal time. 
 
   
   
     17. A method according to  claim 16 , including performing the successive second polarity stress cycles until the voltage differences approach a terminal value, ΔV Terminal . 
   
   
     18. A method according to  claim 15 , further comprising:
 creating a dipole potential monitoring site on said layer with a second polarity corona prior to at least one first polarity corona bias temperature stress cycle; 
 measuring a dipole site voltage at said site before and after at least one second polarity corona bias temperature stress cycle; and 
 correcting said mobile charge according to said dipole site voltages. 
 
   
   
     19. A method according to  claim 15 , further comprising:
 measuring an amount of charge necessary to bias said substrate from a midband condition to a pull-up condition before at least one successive second polarity corona bias temperature stress cycle; 
 measuring an amount of charge necessary to bias said leakage monitoring site back to said midband condition after said at least one successive second polarity corona bias temperature stress cycle; and 
 calculating said mobile charge according to said voltage difference and a difference between said charge measurements. 
 
   
   
     20. A method according to  claim 19 , wherein said midband conditions are determined by a surface photovoltage measurement. 
   
   
     21. A method according to  claim 15 , further comprising:
 measuring a surface photovoltage before and after said second polarity corona bias temperature stress cycle; and 
 determining said mobile charge according to said voltage difference and said surface photovoltage. 
 
   
   
     22. A method according to  claim 15 , further comprising:
 performing successive second polarity stress cycles of substantially equal time until the voltage differences approach a terminal value; 
 creating a dipole potential monitoring site on said layer with a second polarity corona prior to at least one first polarity corona bias temperature stress cycle; 
 measuring a dipole site voltage at said site before and after at least one second polarity corona bias temperature stress cycle; 
 measuring an amount of charge necessary to bias a leakage monitoring site on said substrate from a midband condition to a pull-up condition before at least one second polarity corona bias temperature stress cycle; 
 measuring an amount of charge necessary to bias said leakage monitoring site back to said midband condition after said at least one second polarity corona bias temperature stress cycle; 
 measuring a surface photovoltage before and after at least one of said successive polarity corona bias temperature stress cycles; and 
 correcting said mobile charge according to said dipole site voltages, a difference between said charge measurements and said surface photovoltages.